Well maybe the first gen Charizard, but after that they fixed him.
Oh, I have tons here, I spend literally like hours compiling data for the ugliest Pokemon. After extensive research, I can safely say the ugliest Pokemon is Garbodor.
First of all, the brownish part with the chunks looks like vomit after Halloween with all those candy coloured chunks. Then it's limbs are apparently some weird robotic look, and one hand is totally fingerless for some reason, well it has one finger. Then, it's upper half is supposed to be a garbage bag. But come on, we all know what that is. This Pokemon is quite litterally, Halloween Vomit with green boogers slathered all over it. That's what I see when I see Garbodor.